Abstract: With the deepened exploration progress in the Junggar Basin, the lower assemblage has increasingly become the focus for oil and gas exploration. However, systematic research has not been achieved on the hydrocarbon generation characteristics of the lower assemblage source rocks, and systematic experimental analysis has not been carried out on the hydrocarbon generation potential and oil and gas generation capacity of coaly source rocks with different lithology. Oil and gas have highly yielded in the well of Gaotan 1 in the Gaoquan anticline, and which lithology of coaly source rocks have the closest relationship with it is worth for a further discussion. Sealed vessel autoclave hydrous simulation of Jurassic coaly rock, carbonaceous mudstone and mudstone was carried out in this study, results show that carbonaceous mudstone and mudstone have high oil generation potential. Carbonaceous mudstone is the main contributor of Jurassic coal formed oil, and cutinite may be the main oil source in carbonaceous mudstone. Coaly rock has higher gas generation potential than carbonaceous mudstone and mudstone in higher evolution stage, mainly generating kerogen cracking gas. The carbon isotopic fractionation of simulated gas appears in vary degrees with the increase of evolution, that is, with the increase of maturity, the stable carbon isotope of gas first becomes lighter and then becomes heavier, and the δ¹³C₁ fractionation is more obvious than that of δ¹³C₂. Combined with simulation experiments, the oil and gas source of well Gaotan 1 was further analyzed. It was then concluded that the crude oil of Cretaceous Qingshuihe Formation in well Gaotan 1 is mainly high-mature crude oil generated by Jurassic carbonaceous mudstone, and the three lithologic coaly source rocks contributed to natural gas.